The present invention relates to a hydraulic control apparatus that has a switch valve for controlling supply and drainage of fluid to and from a cylinder, in which the switch valve is switched among a supply position, at which the switch valve supplies fluid from a pump to the cylinder, a drainable position, at which the switch valve drains fluid from the cylinder to the tank, and a neutral position, at which the switch valve does not supply fluid to or drain fluid from the cylinder.
As a hydraulic control apparatus having a switch valve for controlling supply and drainage of fluid to and from a cylinder, a hydraulic control apparatus used in, for example, a forklift is known. Specifically, such an apparatus is used for actuating a lift cylinder for lifting and lowering the fork. The switch valve is switched among a supply position, a drainage position, and a neutral position.
Japanese Laid-Open Patent Publication No. 2006-132680 discloses a hydraulic control apparatus that has an adjusting valve located between a passage connected to a cylinder (cylinder side passage) and a passage connected to a switch valve (switch valve side passage). The regulating valve has a valve body and a fluid chamber. A back pressure chamber of the valve body is exposed to a pilot pressure, so that the valve body contacts a valve seat to shut off a main passage. Further, with the main passage held open, the regulating valve functions as a flow regulator that is capable of controlling the flow rate of fluid by means of flow restricting effect of a space between the edge of the valve body and the fluid chamber. Having the function of an operated check valve and the function of a flow regulator, the regulating valve allows the size of the hydraulic control apparatus to be reduced.
However, in the hydraulic control apparatus according to the above publication, when the regulating valve is forcibly returned to the shutting off position after draining fluid while adjusting the flow rate using the restrictor of the regulating valve, the drainage flow rate is shifted from the restricted state to the shut off state after temporarily being maximized. This can momentarily destabilize the operation of the cylinder.